The impurity spectral
function per orbital and spin, at the Fermi level and \(T=0,\)  is related to
the quasiparticle scattering phase shift \(\delta _{\tau \sigma }\)  by [1]}, [2]}, [3]}, [4]}, [5]}, [6]}
\(\rho _{\tau \sigma }(\omega =0)=-\frac{1}{\pi }\mathrm {Im}G^d_{\tau \sigma }(0)=\frac{1}{\pi \Delta _{\tau }}\sin ^{2}\delta _{\tau \sigma },\) 
